Gift deed on my property

dear experts -

1. I own a flat property in a metro and i am the sole owner of it.

2. i want to execute a gift deed to my father 50% and brother in law 50%

3. do i need to register this deed? how much stamp duty for my relatives?

4. can i mention in the deed that 50% of my father's share will come to me back in future?

Please help me with your answers. thank you!